1. Field of the Invention
This invention relates to the servicing of wells by use of small diameter work strings and more particularly to removal of scale and other downhole deposits from the inside diameter of well tubulars.
2. Description of the Prior Art
It has been common practice for many years to run a continuous reeled pipe (known extensively in the industry as "coil tubing") into a well to perform operations utilizing the circulation of treating and cleanout fluids such as water, oil, acid, corrosion inhibitors, hot oil, nitrogen, foam, etc. Coil tubing, being continuous rather than jointed, is run into and out of a well with continuous movement of the tubing through a coil tubing injector.
Coil tubing is frequently used to circulate cleanout fluids through a well for the purpose of eliminating sand bridges, scale, and similar downhole obstructions. Often such obstructions are very difficult and occasionally impossible to remove because of the inability to rotate the coil tubing and drill out such obstructions. Turbo-type drills have been used but develop insufficient torque for many jobs. Other devices have been used to attempt removal of foreign material from the interior of well tubulars. These well tubulars vary from unperforated and perforated pipe, large diameter casing, production tubing, and slotted or wire-wrapped well liners. Well tubulars often become plugged or coated with corrosion products, sediments and hydrocarbon deposits. The deposits may consist of silicates, sulphates, sulphides, carbonates, calcium, and organic growth.
It is desirable to perform drilling type operations in wells through use of coil tubing which can be run into and removed from a well quickly in addition to performing the usual operations which require only the circulation of fluids. The same types of well servicing can also be performed with various small diameter work strings. The present invention may be used with such work strings and is not limited to coil tubing. For example, a work string consisting of one inch jointed pipe may be insert through a two inch production tubing string to hydraulically clean the inside diameter of five inch casing below the end of the tubing string.
U.S. Pat. No. 3,285,485 which issued to Damon T. Slator on Nov. 15, 1966, discloses a device for handling tubing and the like. This device is capable of injecting reeled tubing into a well through suitable seal means, such as a blowout preventer or stripper, and is currently commonly known as a coil tubing injector. U.S. Pat. No. 3,313,346 issued Apr. 11, 1967 to Robert V. Cross and discloses methods and apparatus for working in a well using coil tubing. U.S. Pat. No. 3,559,905 which issued to Alexander Palynchuk on Feb. 2, 1971 discloses an improved coil tubing injector.
High pressure fluid jet systems have been used for many years to clean the inside diameter of well tubulars. Examples of such systems are disclosed in the following U.S. Pat. Nos.: 3,720,264, 3,811,499, 3,829,134, 3,850,241, 4,088,191, 4,349,073, 4,441,557, 4,442,899, 4,518,041.
Outside the oil and gas industry, tubing cleaners have been used for many years to remove scale and other deposits from the inside diameter of tubes used in heat exchangers, steam boilers, condensers, etc. Such deposits may consist of silicates, sulphates, sulphides, carbonates, calcium, and organic growth.
Wire brushes, scrapers, scratchers and cutters of various designs were among the first tools used to try to remove unwanted deposits. Some of these tools did not reach into the slots or perforations. Those with wires or feelers thin enough to enter the slot or perforation were often too thin to provide much cleaning force. Several types of washing tools are available which use pressurized jets of fluid in an attempt to dislodge undesired material from well tubulars. The development of jet cleaning has advanced from low velocity for use in cleaning and acidizing to abrasive particles suspended in high pressure fluids. Abrasives are used for cleaning flow conductors, but with results less than favorable since the flow conductors are sometimes eroded along with the foreign material plugging or coating the flow conductors.
U.S. Pat. No. 4,625,799 discloses a mechanically indexed cleaning tool. U.S. Pat. No. 4,705,107, discloses the use of boiler type cleaning equipment to clean well tubulars downhole. U.S. Pat. No. 4,781,250 discloses a cleaning tool indexed by fluid pressure changes. Development of apparatus from these patents led to the present invention.
The preceding patents are incorporated by reference for all purposes within this application.